COLUMBIA, S.C. (AP) — Mitt
Romney and Newt Gingrich collided Saturday in the South Carolina
primary, the first Southern testing ground in the race for the
Republican presidential nomination and historically a harbinger of the
final outcome.

Rick Santorum and Texas Rep. Ron Paul rounded out the field in a campaign defined by its unpredictability.

There
were 25 Republican National Convention delegates at stake, but
political momentum was the real prize with the race to pick an opponent
to President Barack Obama still in its early stages.

In all, more
than $12 million was spent on television ads by the candidates and their
allies in South Carolina, much of it on attacks designed to degrade the
support of rivals.

Already, Romney and a group that supports him
were on the air in next-up Florida with a significant ad campaign, more
than $7 million combined to date. The state's primary is Jan. 31.

Interviews
with voters as they left polling places showed nearly half saying their
top priority was finding a candidate who could defeat President Barack
Obama in the fall, followed by wishes for experience, strong moral
character and true conservatism.

In a state with 9.9 percent
unemployment, concern about the economy was high, and almost one-third
of those voting reported a household member had lost a job in the past
three years.

The exit poll was conducted for The Associated Press
and the television networks by Edison Research as voters left polls at
35 randomly selected sites. The survey involved interviews with 1,577
voters and had a margin of sampling error of plus or minus 4 percentage
points.

Romney, the former Massachusetts governor, swept into
South Carolina 11 days ago as the favorite after being pronounced the
winner of the lead-off Iowa caucuses, then cruising to victory in New
Hampshire's first-in-the-nation primary.

But in the
sometimes-surreal week that followed, he was stripped of his Iowa
triumph — GOP officials there now say Santorum narrowly won — while
former Utah Gov. Jon Huntsman dropped out and endorsed Romney and Texas
Rep. Rick Perry quit and backed Gingrich.

Romney responded
awkwardly to questions about releasing his income tax returns, and about
his investments in the Cayman Islands. Gingrich, the former speaker of
the House, benefited from two well-received debate performances while
grappling with allegations by an ex-wife that he had once asked her for
an open marriage so he could keep his mistress.

By primary eve,
Romney was speculating openly about a lengthy battle for the nomination
rather than the quick knockout that had seemed within his grasp only
days earlier.

One piece of primary day theater failed to
materialize when the two men avoided crossing paths at Tommy's Ham House
in Greenville, packed with partisans holding signs that read either
"Romney" or "Newt 2012."

Romney rolled in earlier than expected, and had left by the time Gingrich arrived.

Santorum
got a lift hours before the polls closed when the Iowa Republican Party
declared him the winner of the caucuses on Jan. 3. Romney was
pronounced the victor by eight votes initially, but on Thursday, party
officials said a recount showed Santorum ahead by 34. Even so, they
declared the outcome a tie.

Santorum, a former Pennsylvania
senator, pinned his South Carolina hopes on a heavy turnout in parts of
the state with large concentrations of social conservatives, the voters
who carried him to his surprisingly strong showing in Iowa.

Paul
had a modest campaign presence here after finishing third in Iowa and
second in New Hampshire. His call to withdraw U.S. troops from around
the world was a tough sell in a state dotted with military installations
and home to many veterans.

As the first Southern primary, South Carolina has been a proving ground for Republican presidential hopefuls in recent years.

Since Ronald Reagan in 1980, every Republican contender who won the primary has gone on to capture the party's nomination.

Romney's
stumbles began even before his New Hampshire primary victory, when he
told one audience that he had worried earlier in his career about the
possibility of being laid off.

He gave a somewhat rambling,
noncommittal response in a debate in Myrtle Beach last Monday when asked
if he would release his tax returns before the primary. The following
day, he told reporters that because most of his earnings come from
investments, he paid about 15 percent of his income in taxes, roughly
half the rate paid by millions of middle-class wage-earners. A day
later, aides confirmed that some of his millions are invested in the
Cayman Islands, although they said he did not use the offshore accounts
as a tax haven.

Asked again at a debate in North Charleston on
Thursday about releasing his taxes, his answer was anything but succinct
and the audience appeared to boo.

Gingrich benefited from a shift
in strategy that recalled his approach when he briefly soared to the
top of the polls in Iowa. At mid-week he began airing a television
commercial that dropped all references to Romney and his other rivals,
and contended that he was the only Republican who could defeat Obama.

It
featured several seconds from the first debate in which the audience
cheered as he accused Obama of having put more Americans on food stamps
than any other president.

Nor did Gingrich flinch when ex-wife
Marianne said in an interview on ABC that he had been unfaithful for
years before their divorce in 1999, and asked him for an open marriage.

Asked
about the accusation in the opening moments of the second debate of the
week, he unleashed an attack on ABC and debate host CNN and accused the
"liberal news media" of trying to help Obama by attacking Republicans.
His ex-wife's account, he said, was untrue.